Body heat, fermentation drive drug-delivery micropump

This diagram shows a new type of miniature pump activated by body heat that could be used in drug-delivery patches powered by fermentation. The micropump works by harnessing the pressure generated by fermenting yeast. Such drug-delivery patches might use arrays of microneedles to deliver a wider range of medications than now possible with conventional patches. Image: Purdue University/Manual Ochoa

Researchers have created a new type of miniature pump
activated by body heat that could be used in drug-delivery patches powered by
fermentation.

The micropump contains Baker's yeast and sugar in a small
chamber. When water is added and the patch is placed on the skin, the body heat
and the added water causes the yeast and sugar to ferment, generating a small
amount of carbon dioxide gas. The gas pushes against a membrane and has been
shown to continually pump for several hours, says Babak Ziaie,
a Purdue University professor of electrical and computer engineering and biomedical
engineering.

Such miniature pumps could make possible drug-delivery
patches that use arrays of "microneedles" to deliver a wider range of
medications than now possible with conventional patches. Unlike many other
micropumps under development or in commercial use, the new technology requires
no batteries, said Ziaie, who is working with doctoral student Manuel Ochoa.

"This just needs yeast, sugar, water and your own body
heat," Ziaie says.

The robustness of yeast allows for long shelf life, and the
design is ideal for mass production, Ochoa said.

"It would be easy to fabricate because it's just a few
layers of polymers sandwiched together and bonded," he says.

Findings were detailed in a research paper published online
in Lab on a Chip. The paper was written by Ochoa and Ziaie, and the
research is based at Purdue's Birck Nanotechnology Center in
the university's Discovery Park.

The "the microorganism-powered thermopneumatic
pump" is made out of layers of a rubberlike polymer, called
polydimethylsiloxane, which is used commercially for diaphragms in pumps. The
prototype is 1.5 cm long.

Current "transdermal" patches are limited to
delivering drugs that, like nicotine, are made of small hydrophobic molecules
that can be absorbed through the skin, Ziaie says.

"Many drugs, including those for treating cancer and
autoimmune disorders cannot be delivered with patches because they are large
molecules that won't go through the skin," he says. "Although
transdermal drug delivery via microneedle arrays has long been identified as a
viable and promising method for delivering large hydrophilic molecules across
the skin, a suitable pump has been hard to develop."

Patches that used arrays of tiny microneedles could deliver
a multitude of drugs, and the needles do not cause pain because they barely
penetrate the skin, Ziaie says. The patches require a pump to push the drugs
through the narrow needles, which have a diameter of about 20 microns, or
roughly one-fourth as wide as a human hair.

Most pumps proposed for drug-delivery applications rely on
an on-board power source, which is bulky, costly, and requires complex
power-management circuits to conserve battery life.

"Our approach is much more simple," Ziaie says.
"It could be a disposable transdermal pump. You just inject water into the
patch and place it on your skin. After it's used up, you would throw it
away."

Researchers have filed an application for a provisional
patent on the device.